1. Field of the Invention
The invention disclosed herein relates to switching power supply devices.
2. Description of Related Art
Conventionally, a switching power supply device is designed around a controller IC as its core, with various discrete components externally fitted to it.
However, with conventional switching power supply devices, while many examples of design are proposed for constant-voltage power supply circuits, very few examples of design are known for constant-current power supply circuits. Thus, in applications that require a stabilized output current (such as LED (light-emitting diode) lighting devices and battery charging devices), a constant-current power supply circuit needs to be provided separately in the stage succeeding a constant-voltage power supply circuit, inconveniently resulting in increased cost and diminished efficiency.
Incidentally, Patent Document 1 (Japanese Patent Application published as No. 2005-142137) proposes a circuit configuration for furnishing a direct-current power supply device (in particular, an IPD control circuit in it) additionally with a constant-current control function. However, Patent Document 1 gives no consideration to a no-load or low-load condition (a state of the load that makes the output current zero or nearly zero), and thus leaves room for improvement.